To assess the status of a saphenous vein (SV) excised for coronary artery bypass grafting (CABG), 3,394 cm of the remnant SV from 402 patients who underwent CABG were examined. The SV remnants were 0.5 to 52 cm long (mean 8.4). They were sectioned into 5-mm-long segments, and the resulting 6,788 five-millimeter segments were examined histologically: 5,896 (87%) were narrowed 0 to 25% in cross-sectional area by fibrous tissue; 853 (12%) were narrowed 26 to 50%; 23 (0.6%), 51 to 75%, and 16 (0.4%) segments were narrowed 76 to 100%. Of the 16 segments severely narrowed, 7 (44%) were nearly totally occluded by fibrous tissue. In 17 patients who died within 24 hours of CABG, similar degrees of luminal narrowing were observed in remnant segments and in utilized segments of SV. Thus, significant preexisting luminal narrowing of SV used for CABG is infrequent. The intimal fibrous thickening is variable within the same vein when each 5-mm-long segment is analyzed; it is variable from 1 vein to another in the same patient, and it varies among patients.